subprocess.call env var

I'm using Popen because I need the env, like this:

Popen(
    ["boto-rsync", "..."],
    env={"PATH":"/Library/Frameworks/Python.framework/Versions/2.7/bin/"},
    )

The problem is Popen runs the command as a new thread. Is there any way that I could pass the env to subprocess.call or prevent Popen from creating a new thread? Thanx